The present invention relates generally to the field of vehicular brake systems. More particularly, the invention relates to an apparatus and method for backdriving a brake caliper.
Virtually all wheeled vehicles utilize braking systems to selectively inhibit wheel rotation and, therefore, reduce vehicle speed. Braking may be accomplished by the use of a disc braking system whereby a friction force is applied at one or more wheel assemblies to inhibit wheel rotation. Numerous disc brake systems are known in the art. The systems generally include a rotor or disc secured to the vehicle wheel, a caliper assembly mounted to the vehicle chassis, and a pair of friction pads disposed on opposing sides of the rotor. Upon activation of the disc brake system, the caliper moves the friction pads toward one another into frictional engagement with the rotor actuating braking force and slowing the vehicle. When the brake is released, the caliper moves (e.g., backdrives) the friction pads out of frictional engagement with the rotor allowing free tire rotation.
Brake-by-wire braking systems may include an electrically powered caliper to actuate braking. Typical electrical caliper designs utilize high gain mechanisms to generate a large clamp load with relatively small motor actuators. During certain conditions, the electrically powered caliper may experience brake xe2x80x9clock-upxe2x80x9d. For example, failure or power loss of the caliper during a brake apply may produce sustained rotor clamp load. This may inappropriately cause brake drag or prevent the vehicle tire from rotating altogether. Accordingly, it would be desirable to provide a strategy for backdriving a caliper to prevent brake xe2x80x9clock-upxe2x80x9d during such conditions.
Repeated brake apply cycles may wear friction pads thereby reducing their overall thickness. Many brake caliper designs compensate for friction pad wear wherein the extent of caliper backdrive is continuously diminished. This permits the friction pad surface to remain in a working proximity to the rotor. Accordingly, it would be desirable for a backdriving strategy to compensate for friction pad wear.
Therefore, it would be desirable to provide an apparatus and method for backdriving a brake caliper that would overcome the aforementioned and other disadvantages.
One aspect of the present invention provides a brake caliper backdrive apparatus. The apparatus includes a brake caliper, a motor including a shaft operably attached to the brake caliper and, a biasing member operably attached to the shaft. The biasing member backdrives the motor thereby releasing the brake caliper. The biasing member may be a clock spring and may be sized to backdrive a failed motor. The assembly may further include a flange portion operably attached to the brake caliper and the biasing member, wherein the brake caliper release unclamps the flange portion thereby adjusting the biasing member.
Another aspect of the invention provides a method of backdriving a brake caliper. The method includes rotating a shaft to clamp the brake caliper, storing energy in a biasing member responsive to the shaft rotation, and reversing the shaft rotation using the stored energy. The shaft rotation may be reversed during a condition of motor failure, such as a power loss. Reversing the shaft rotation may release the brake caliper. The method may further include compensating for friction pad wear, such as by adjusting the biasing member.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.